Thanks for all the replies. I don't change my oil myself. I will have it serviced. So, longer intervals for me would be better..My driving habits are tame. Around town and highway driving once or twice a week, nothing severe and no towing. I will always use a good filter. Even though I'm a female, I seem to know more about cars than the men in my life. So the guys come to me for reseach:)
My average mpg is only 17. I know it's a new engine and maybe takes times to break in ,but I was hoping for a little better gas mileage, hence the possible switch to syn. I want to put a little ucl lucas or mmo in the gas to maybe improve but I'm kind of afraid to ruin anything. Regular use of fuel additives have kept older cars running well.